Face recognition has numerous security-related applications such as user identification, user authentication for online and offline resource accesses, door and gate unlocking.
Conventionally, face recognition methods use a real-time captured image of the subject's face to find a match in a library of previously captured facial images. The face matching process is relatively accurate in comparison to other biometric identification methods with well-developed and tested facial feature analysis techniques. In general, the techniques extract characteristic data of a face region as shown in FIG. 1, which is unique for each person, from the captured image of the subject's face, and compares the characteristic data against those stored in the library, thereby matching the subject's face to that of a previously registered person.
Some face recognition systems have been developed to determine whether the subject is a living person by ways of requiring the subject to make multiple facial expressions and movements during an identification session and allowing the system to detect and capture the multiple frames of facial expressions and movements for matching. For example, U.S. Pat. No. 6,922,478 disclosed a method for verifying the authenticity of a captured image of a person comprising recording a sequence of consecutive individual images of the person and determining the authenticity of the recorded images by checking if at least in two consecutive individual images of the sequence intrinsic movements can be detected. However, such an authenticity verifying system may be deceived by printed photographs or an electronic display showing images of the subject to be authenticated as illustrated in FIG. 2.
Other face recognition systems have been developed to determine whether the captured face image is of a living body by ways of requiring interactive inputs from the subject to be recognized. For example, European Patent No. 1990770 disclosed a face authenticating apparatus includes a presentation pattern display unit provided at a different position from a key input unit to display an instruction for a user to input a key pattern during facial authentication; and an image capturing unit for capturing the face of the user and/or a movement of a portion of the face of the user during a portion of or the entire time from when the presentation pattern display unit displays the instruction to when the key input is completed. And from process executed by the apparatus, determine whether the captured face image is of a living person. However, the requirement for interactive inputs limits its applications, usefulness, and the types of users.
Improvements have been made to tackle the photo spoofing and facemask spoofing by ways of checking the three-dimensional (3D) perspective features of the face of the subject. For example, U.S. Pat. No. 9,619,723 disclosed a process of 3D perspective check comprising collecting two or more images of the subject's face. The two or more images of the subject's face are then used to calculate the stereoscopic view data of the subject's face. However, such a face recognition system could produce false rejection if the subject maintains perfect face alignment with the camera center as illustrated in FIG. 3.